This invention relates to aluminum products, and particularly to aluminum products having improved corrosion resistance, as well as a process for making such products.
Corrosion resistance is a concern common to many aluminum components used in a variety of applications. For example, road salt and moisture often cause perforation of automotive radiators.
It has been known for many years that corrosion problems in brazing can be alleviated to some extent by adding an interlayer between the structural member portion or core and the brazing layer. Such an interlayer is described, for instance, in Miller U.S. Pat. No. 2,821,014. The problem of corrosion in vacuum brazing is particularly considered in Singleton et al U.S. Pat. No. 3,788,824, where iron is added to either the core alloy or the cladding alloy to provide corrosion resistance and sag resistance. Various other patents such as U.S. Pat. Nos. 4,039,298, 4,093,782, 3,994,695, 4,339,510 and 4,649,087 describe various combinations of alloying components particularly for the core alloy which are claimed to provide benefit in intergranular corrosion resistance.
In Nakamura, U.S. Pat. No. 4,172,548, a procedure is described for controlling corrosion following vacuum brazing by controlling the grain size of the brazing sheet to at least 60 microns in diameter, this being achieved by a controlled cold work followed by a full anneal.
Finnegan et al, U.S. Pat. No. 4,586,964 also considers the problem of corrosion in a vacuum brazed product and suggests a technique in which an interanneal is provided before a controlled cold work. This controlled cold work is maintained within a certain range of reduction.